DOS was a command line operating system that existed before and during some of the early Windows. It was used to launch Windows, but could run on its own, which Windows could not do until about the year 2000, although many people believe that Windows did away with DOS in 1995.

While it is true that Windows streamlined the booting of the operating systems when they finished with their support of Windows 3.11, DOS was still the basic operating system upon which Windows was built until ME came out. The removal of DOS, and the associated difficulty that Windows had with its machine code, was one of the huge problems that caused ME to fail so hard, although the more robust Windows 2000 made itself known.

In some circles, Windows is considered to be a very, very new operating system because up until Windows ME they were closer to being a window manager, similar to the way that any given distribution of linux could have xfce, gnome, kde, etc. to manage the GUI. The biggest difference between linux window managers and Windows is that Windows didn't allow any other window manager to be installed on the system, and would destroy the DOS operating system if it was removed.

@kbw: If you don't know where to begin, it's probably because you don't know. I was using and building in DOS before the i386 came out, and I've used it from then until the last time Microsoft employed it in Windows 98.

@retsgorf297:
MS-DOS was the launchpad that I described. DOS existed before Bill Gates started programming, and it was completely independent of any other operating system. MS-DOS was a modified version of DOS that was only designed to start Windows, and wasn't used until Windows 3.

MS-DOS was a modified version of DOS that was only designed to start Windows

Microsoft DOS wasn't invented to launch Windows. It was "developed" as the O/S for IBM's new personal computer back in 1981. The idea of building Windows on top of it (using its file system services) only happened later (with Windows 1.0 in 1995.)

(I used "developed" (in quotes) as I knew Microsoft bought a more or less finished version of DOS from another company, but didn't recall who it was. Thanks to Wikipedia.org, I now know it was Seattle Computer Products. Microsoft bought 86-DOS (aka Q-DOS) and renamed it to MS DOS; so "MS DOS" did predate Microsoft! To confuse matters, IBM then sold it on as PC-DOS.)

It was used to launch Windows, but could run on its own, which Windows could not do until about the year 2000,

16-bit versions of Windows (up to Windows 3.1) ran on top of DOS. That is, they relied on DOS for file and disk access. You needed a DOS installation for old 16-bit versions of Windows to run.

With Windows 95, etc, DOS was relegated to just handling 16-bit drivers; Windows took over file system handling, and handled 32-bit device drivers itself (VxDs). And you didn't have to install DOS separately; it was provided as part of the overall Windows installation, allowing you to boot in command line "DOS" mode.

But Windows NT 3.1 was released in 1993 -- and it never relied on DOS. So some versions of Windows have been running DOS-free since the early 1990's.

When you run a 16-bit program on Windows NT or the 32-bit versions of modern Windows, it's being run by WOW (the Windows on Windows) compatibility layer. (64-bit versions of Windows don't support WOW; just WOW64, which allows 32-bit apps to run on 64-bit Windows.)

(With Windows 98 and Windows 2000, the Windows Driver Model took over from VxDs and the Windows NT driver model. WDM is actually an enhanced version of the NT model.)

Andy

PS The current version of Windows evolved from Windows NT not Windows 95. Some the code was common, mostly in the user layer, but the kernels of Windows NT and Windows 95 were radically different. And it's the Windows NT kernel which was taken forwards.

as per as I know DOS is not an operating system bt my professor is saying that DOS is an operating system....

MS-DOS (DOS for short) was an operating system. Windows came along as a Graphical User Environment (or graphical shell) siting on top of DOS. Then Microsoft had the idea of making Windows the Operating System. It did this with Windows NT 3.1. They gave Windows NT a Command Line Interface (Text Shell).

So now at the same time you had Windows (a dos based OS with a Graphical shell) and Windows NT (with a CLI).

So now comes the confusion. In Windows you used to open a 'DOS Box', a command line interface to interact with DOS. This set the idea that window that you type text commands in is called DOS. For some reason this misconception lives on.

kbw: If you don't know where to begin, it's probably because you don't know. I was using and building in DOS before the i386 came out, and I've used it from then until the last time Microsoft employed it in Windows 98.

Then you ought to know better than posting gems like:

"It was used to launch Windows, but could run on its own."

"and [Windows] would destroy the DOS operating system if it was removed."

"MS-DOS was a modified version of DOS that was only designed to start Windows"

DOS is still an OS for special uses. For example, a HDD/SDD vendor can pack a firmware update with a DOS variant. You get a bootable media tailored to run a single application in minimal environment (to avoid interference).

DOS had a command interpreter (aka command prompt, shell) "command.com". Later Windows have "cmd.exe", but I prefer an open source "sh.exe". However, a shell is simply a CLI for interacting with (subset of) an OS.